1. Field of the Invention
The present invention relates to a screw member fastened by a rotary tool (a driver) and, particularly, relates to a screw member properly used for an implant treatment in a dental field.
2. Description of the Conventional Art
A lot of screw members are widely used for an implant treatment in a dental field. More particularly, screw members used in an implant treatment called a two time method will be described as follows. A cover screw is temporarily fastened to an implant fixture, and protects the intraoral side of the implant fixture. The cover screw is used until osseointegration (synostosis) between the implant fixture and a bone is completed after embedding the implant fixture in a primary operation. A healing abutment is temporarily fastened on the intraoral side of an implant exposed by opening a gingiva in a secondary operation, and promotes gingival plasty. A guide pin is used for fastening an impression coping to an implant fixture when collecting an impression for producing a dental prosthesis after the secondary operation. An abutment screw is used to fasten an abutment to an implant fixture. A gold screw is used for fastening a gold cylinder to an abutment, where the gold cylinder becomes to be a base for fixing a dental prosthesis. A soldering screw is used for fastening a gold cylinder to an abutment, where the gold cylinder becomes to be a base for fixing a dental prosthesis when a dental technician produces the dental prosthesis.
Such the screw members are fastened to screw holes of a member, such as an implant fixture, by a rotary tool engaged with an engagement part provided at a head part. However, since this operation is generally carried out in an oral cavity of a patient, the operation for fastening the screw member needs to be carried out in a state that a center axis of the screw hole completely agrees with a center axis of the screw member. Thus, the screw member needs to be moved to a position where the center axis of the screw member completely agrees with the center axis of the screw hole.
Since a screw members cannot be handled directly by hand due to a hygienical reason generally in an implant treatment, the screw member is moved to the screw hole of a member to be fastened in a state of being held with the rotary tool. However, there is a problem that the screw member is dropped in an oral cavity of a patient when moving the screw member.
Further, in many cases, the screw members need to be unfastened and removed after being fastened once. However, the unfastened screw member needs to be easily taken out from the oral cavity in a state of being held with the rotary tool.
In order to solve these problems in the implant treatment, for example, Japanese Translation of PCT Publication No. 2001-500768 discusses a technique to improve ability for making a screw member to be held on a rotary tool. This technique uses wedge effect generated at a head part side end edge of a hole when a top end part of a tapered rotary tool is inserted into a hole formed at a head part of the screw member.
However, when the top end part of the rotary tool is inserted into the hole formed at the head part of the screw member with strong force in order to hold the screw member with the rotary tool, an engagement portion of the head part side end edge of the hole formed at the head part of the screw member may be scratched. When the engagement portion is scratched, the wedge effect is not generated between the screw member and the rotary tool, so that the screw member cannot be moved in a state of being held with the rotary tool. Particularly, as for a screw member which needs to be unfastened and removed after being fastened once, e.g., the cover screw, the top end part of the rotary tool is inserted at least two times into a hole formed at the head part of the screw member with strong force. Thus, the engagement portion of the head part side end edge of the hole formed at the head part of the screw member is scratched, so that a probability that the screw member can not be moved in a state of being held with the rotary tool is high.